The Steps for Using Polyferric Sulfate in Phosphorus Removal

Phosphorus is a major contributor to eutrophication in water bodies, and its removal from wastewater is essential to protect aquatic ecosystems.  Polyferric sulfate (PFS) is a highly effective coagulant widely used for phosphorus removal due to its efficiency and cost-effectiveness.  This article outlines the steps for using PFS in phosphorus removal, divided into two main phases: preparation and application.

Preparation Phase: Polyferric Sulfate Dosage and Solution Preparation

The first step in using polyferric sulfate for phosphorus removal is to determine the appropriate dosage and prepare the polyferric sulfate solution.  The dosage of PFS depends on factors such as the initial phosphorus concentration, the pH of the wastewater, and the presence of other contaminants.  Laboratory jar tests are often conducted to determine the optimal dosage, which typically ranges from 10 to 50 mg/L, depending on the specific conditions of the wastewater.

Once the dosage is determined, the polyferric sulfate solution is prepared.  PFS is usually supplied in liquid or solid form.  If using solid polyferric sulfate, it must be dissolved in water to create a concentrated solution, typically with a concentration of 5-10%.  The solution is then diluted further before being added to the wastewater.  Proper mixing equipment, such as a stirrer or mixer, is essential to ensure the PFS is fully dissolved and evenly distributed.

Application Phase: Polyferric Sulfate Coagulation and Sedimentation

The application phase involves the actual addition of PFS to the wastewater and the subsequent coagulation and sedimentation processes.  The prepared polyferric sulfate solution is injected into the wastewater stream using a dosing pump or similar equipment.  The injection point is typically located in a rapid mixing tank to ensure thorough dispersion of the coagulant.

After the addition of polyferric sulfate, the wastewater undergoes rapid mixing to promote the destabilization of colloidal particles and the formation of microflocs.  This is followed by slow mixing, which allows the microflocs to aggregate into larger, denser flocs that can capture phosphate ions and other suspended solids.  The coagulation process is highly dependent on maintaining the optimal pH range (5-7), as this ensures maximum efficiency in phosphorus removal.

Once the flocs have formed, the wastewater is transferred to a sedimentation tank or clarifier.  Here, the flocs settle to the bottom due to their increased density, separating from the treated water.  The settled sludge, containing the removed phosphorus, is then collected and disposed of or further processed.  The clarified water, now with significantly reduced phosphorus levels, can be discharged or subjected to additional treatment if necessary.

Using polyferric sulfate for phosphorus removal is a straightforward and effective process that involves careful preparation and precise application.  By determining the correct dosage, preparing the PFS solution, and ensuring proper coagulation and sedimentation, wastewater treatment plants can achieve high phosphorus removal efficiencies.